Disable purchasing credit

[s0me0ne-unkn0wn]

Closes #4454

[paritytech-cicd-pr]

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[seadanda]

I don't agree with the approach here - I think we should disallow the calls using the BaseCallFilter in the runtimes, rather than commenting stuff out in the broker pallet.

This way could lead to version issues later - we will want to enable this at different times for each network, but potentially still want features/fixes that are added at later points. This could mean that we would need to maintain two versions of the pallet - one with purchase credit active, and one without.

[bkchr]

I don't agree with the approach here - I think we should disallow the calls using the BaseCallFilter in the runtimes, rather than commenting stuff out in the broker pallet.

Yes, this 10000%. Also we should just get implement the credit system, as it is not that complicated.